Field of the Invention
The present invention relates to a golf ball, and more particularly to a golf ball capable of improving a carry distance.
Description of the Related Art
Generally, dimple arrangement of a golf ball has a great influence on flight performance of the golf ball. Specifically, when a golfer hit a golf ball with a golf club, back spin is generated by the loft angle of the golf club, at the same time strong repulsive elasticity is generated from the core of the golf ball and launching the ball, thus the golf ball flies while forming various type ballistic trajectories depending on specifications of the golf ball.
If a golfer hit a golf ball with a driver, the flight duration of the golf ball is about 6 seconds. Although the ballistic trajectory of the golf ball at the initial stage is similar, the peak of the ballistic trajectory is considerably different according to dimples of the golf balls. Of course, even if the same golfer hit a golf ball using the same golf club, flight characteristics of the golf ball is different due to differences in repulsive elasticity, hardness and rotating performance of the golf ball, the flight characteristics and the flying trajectory of the golf ball are also various according to size, number, area ratio, depth, arrangement of dimples, and so on.
Further, divisional composition used when dimples are arranged is a very important factor determining the size and area ratio of the dimples in connection with symmetry of a golf ball. Generally, divisional composition to arrange dimples on the surface of a golf ball serves to divide a sphere into a spherical polyhedral state. That is, as divisional composition, there are a spherical tetrahedron composed of 4 spherical triangles, a spherical hexahedron composed of 6 spherical squares, a spherical octahedron composed of 8 spherical triangles, a spherical cube-octahedron composed of 6 spherical squares and 8 spherical triangles, a spherical dodecahedron composed of 12 spherical pentagons, a spherical icosahedron composed of 20 spherical triangles, a spherical icosi-dodecahedron composed of 12 spherical pentagons and 20 spherical triangles, and so on. They may be subdivided and thus form spherical polyhedron of various shapes and then, dimples may be arranged.
For example, U.S. Pat. No. 5,575,477 discloses a golf ball in which, in arrangement of dimples on its spherical surface divided into faces of an icosi-dodecahedron, balance is achieved between the dimple-free area ratio of equatorial region (mold parting line), generated by buffing, and the dimple-free area ratio of the polar regions, generated by widely arranging dimples by new composition, so as to promote flight stability and to improve the carry distance of the golf ball. However, the disclosed golf ball has excellent flight stability but has disadvantages, such as increase in flight duration and difficulty in raising a ballistic trajectory peak.
And U.S. Pat. No. 5,564,708 discloses a golf ball in which the largest dimple is arranged respectively to apex portion of spherical triangle forming an octahedron and apex of small spherical triangle (one small spherical triangle in a spherical cube-octahedron) formed by connecting midpoint of each side of large spherical triangle one another, so that large and small dimples being arranged on each polygon are balanced to uniform air resistance and thus, flight stability of the golf ball is improved.
Further, U.S. Pat. No. 5,024,444 discloses a golf ball in which three or four kinds of dimples are arranged on the surface of the golf ball, and the carry distance of the golf ball is increased by properly adjusting a ratio between diameters of the dimples and depths of the dimples by adjusting the depths of the dimples according to the diameters of the dimples.
Meanwhile, U.S. Pat. No. 6,450,902 discloses a dimple arrangement of a golf ball in which conventional divisional composition of a spherical cube-octahedron is further subdivided such that dimples in regions are connected to the largest size dimples which exist one by one in the regions in a form of band and thus, a region of an air stream reducing air resistance in a low-speed area is provided so as to increase the carry distance of the golf ball.
Even in case of other documents than the above-described Patents, dimples are generally arranged in order in consideration of the sizes of the dimples so as to achieve symmetrical divisional composition and uniform arrangement of the dimples.
In this case, when hit a golf ball with a golf club, back spin is similarly generated by the loft angle of the head of the golf club. In this way, air pressure is accumulated below the reversed rotating ball, and air above the golf ball flows faster than peripheral air and thus air pressure above the golf ball is lowered. Consequently, aerodynamic lift equivalent to many times of gravity is formed on the golf ball. Thereafter, the golf ball flies at a high speed up to the apex of a ballistic trajectory with the aid of repulsive power to hitting power and aerodynamic lift, and flies at a low speed from the apex of the ballistic trajectory to a landing point. Therefore, if the time taken for a golf ball to reach the apex of the ballistic trajectory is further increased or the apex is further raised even when the golf ball flies along a proper trajectory for the same time, the carry distance of the golf ball may be further increased based on the principle of parabolic motion.
However, since air resistance of the golf ball increases in proportion to the maximum sectional area of the golf ball, decrease in size of the golf ball is advantageous in terms of the carry distance. However, the sizes of golf balls are restricted to 1.68 inches or more by the official ball regulations of R&A or USGA and thus, the sizes of golf balls should not be discretionally adjusted.
Therefore, most authorized golf balls are about 1.68 inches in diameter, the surfaces areas of the golf balls according to diameters thereof are similar and thus, if dimples are arranged by dividing the surfaces of a sphere—into the above-described spherical polyhedrons, the spherical polyhedrons are indispensably overlapped.
In general, in manufacture of a golf ball, if a cavity inserted into a mold is manufactured, a master mold is firstly made and then covered with a stainless steel plate having a thickness of 0.8 mm or less, and dimples are formed respectively by pressing using high-pressure pins. In this case, the depth of the dimples is restricted to some degree by the diameter of the dimples due to strength of the stainless steel plate. If such a depth is converted into a Frustum depth and thus, a volume ratio of the dimples is calculated, the volume ratio of dimples in most golf balls are about 400 mm3±10%. Accordingly, in case of dimples formed in such a cavity, the diameters of the dimples are determined, the volume ratio of the dimples become almost similar, flying characteristics of a golf ball are determined by the sizes and the number of respective dimples. Furthermore, when dimples are arranged, the maximum number of dimples generally fills on the surface of a sphere, a dimple area ratio tends to be determined by the diameters and the number of the dimples. It may support explanation that, if the total number of dimples having similar sizes is the same, the flying performances of golf balls become similar in terms of dimple arrangement determining the carry distance of the golf ball aerodynamically.
Of course, even if a golf ball has the same dimple arrangement, the flying performance of the golf ball differs from that of other golf balls due to differences in the structure, size, weight, and the compression of a golf ball, a material and hardness of a cover, and a degree of repulsive elasticity of a core. However, if dimple arrangements having symmetry according to the official ball regulations of R&A or USGA are formed by equalizing structures, sizes, weight, and hardnesses of golf balls, and cover materials and uniformizing the total numbers of dimples having similar sizes, when the golf balls manufactured having different dimple arrangements are hit by a swing machine and tracked using a track-man or through other measurement methods, the flying performances of the golf balls are not significantly different.
The important factors in the flying performance of a golf ball are carry distance, amount of rotation, flight duration, peak height, and lateral deviation. If two golf balls having 3˜6 kinds of dimples of different sizes, which are arranged in the same numbers, have different dimple arrangements according to dimple size, the peak heights and the lateral deviations of the two golf balls are different due to a difference of the dimple arrangements.
Meanwhile, a golf ball needs to have symmetry according to the official ball regulations, that is why the same dimples are arranged on the same spherical polygons so that the surface of a sphere is symmetrically divided into a spherical polyhedron consisting of a plurality of spherical polygons. In this case, if the surface areas of the spherical polygons forming the spherical polyhedron are the same, there is no difference between dimple arrangements and a difference between flying performances is restricted. However, in many cases, the surface areas of spherical polygons formed according to divisional composition are greatly different, thus causing difficulty in dimple arrangement.
For example, if the radius of a golf ball is 0.84 inches, the overall surface area of the golf ball is 8.866831105 in2. In case of a spherical rhombic dodecahedron, 12 spherical rhombi, each of which has a surface area of 0.738902592 in2, form the overall surface area of a sphere. However, in case of a spherical cube-octahedron, the surface area of one of spherical triangles forming the spherical cube-octahedron is 0.388987121 in2 and the surface area of one of spherical squares forming the spherical cube-octahedron is 0.959155691 in2, and 8 spherical triangles and 6 spherical squares form the overall surface area of a sphere divided into the spherical cube-octahedron. Further, in case of a sphere of a spherical icosi-dodecahedron having the same radius, the surface area of one of spherical pentagons is 0.527394879 in2, the surface of one of spherical triangles is 0.126904631 in2, and 12 spherical pentagons and 20 spherical triangles form the overall surface area of the sphere. In this way, the respective spherical polygons are different and thus, the surface areas thereof are different. If a dimple arrangement in which only 1 kind of relatively large dimples having a diameter 0.145 inches or more to easily obtain the aerodynamic lift are symmetrically arranged on the overall surface of a sphere is given, an excessively large number of land regions without dimples is formed, the total area ratio of the dimples is reduced and thus, aerodynamic lift is reduced and an expected carry distance of the golf ball may not be obtained. On the other hand, if a dimple arrangement in which only small dimples having a diameter 0.1 inches or less are symmetrically arranged on the overall surface of a sphere is given, a serious problem in aerodynamic lift is generated and thus, only about 85% of a desired carry distance of the golf ball may be acquired.
Therefore, in order to solve the above-described problems, a dimple arrangement, in which various kinds of dimples having different sizes are arranged on the surface of a golf ball so as to minimize regions without dimples, retain lateral symmetry, and promote flight stability of the golf ball, has been required.